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STEPS … A T CY Pr ogr am _______________________________________________________________________________________ LECTURE NOTES – BIOLOGY
CONTROL & COORDINATION 1.
Parthenocarpy:- Auxins play an important role in the development of fruits without
pollination
and
fertilization.
This
phenomenon
is
known
as
parthenocarpy. Fruits produced by this method are called parthenocarpic or seedless fruits. 2.
Synapse:- The loose connection between the axon endings of one nerve cell and cyton of the next nerve cell is called synapse. In other words, signals travel from one neuron to another neuron across a junction called synapse. Structure of the synapse The neurons do not touch at the synapse. There is a space between adjacent neurons called the synaptic cleft. The synaptic cleft is about 20 mm in width. The axon terminal of a presynaptic neuron has a bulb – like appearance known as synaptic bulb.
Structure of the synapse
3.
Homeostasis:- The capacity of an organism to adjust itself to cope with the external stress and maintain a steady state of functioning is referred to as homoeostasis. (Latin: homeo means similar, statis means situation) Homeostasis in a multicellular organism is achieved in two ways. 1.
By the endocrine system
2.
By the nervous system
Both hormones and nerve impulses coordinate the body’s activities, but they do so in different ways.
STEPS____________________________________________________________ 1 Get free chapterwise tests for Class Xth on www.tcyonline.com
STEPS … A T C Y P r og r am _______________________________________________________________________________________ LECTURE NOTES – BIOLOGY
4.
Endocrine glands: endo means within, krinein means to separate. As these glands do not have their own ducts, the secretions of such glands, hormones, are released directly into the tissue space next to each endocrine cell and are carried by blood or lymph to the target organ.
Blood flow
Glands with and without ducts 5.
Efferent nerve:- Motor or efferent nerve which carries the message from the spinal cord to the muscles or glands (effector organ)
6.
Afferent nerve:- Sensory or afferent nerve which carries the message from receptor to the spinal cord.
7.
Neurotransmitters:- The transmission across a synapse is by chemical means. The synaptic bulb contains chemicals known neurotransmitters. When a nerve impulse (action potential) arises at the axon terminal, it causes synaptic bulbs
to
release
neurotransmitters
in
the
synaptic
cleft.
These
neurotransmitters diffuse easily across the synaptic cleft. In this way, the impulse is transmitted to another nerve cell or neuron. There are many neurotransmitters
but
the
principle
ones
are
acetylcholine
and
norepinephrine. 8.
Names of Pythohormones:- There are five main types of naturally occurring plant growth regulators. 1.
Auxins
2.
Gibberellins
3.
Kinins
4.
Ethylene
5.
Abscisic acid (ABA)
2 STEPS____________________________________________________________ Get free chapterwise tests for Class Xth on www.tcyonline.com
STEPS … A T CY Pr ogr am _______________________________________________________________________________________ LECTURE NOTES – BIOLOGY
9.
Differences between sympathetic and parasympathetic nervous systems Parasympathetic nervous system
Sympathetic nervous system
The nerve fibres originate in the middle The nerve fibres originate from the brain portion – thoracic and lumbar region, of the and lower (sacral) region of the spinal cord. spinal cord. The ganglia are in a chain running parallel The ganglia are near or in the target organ. and close to spinal cord. Inhibitory (calming down) effect.
Stimulatory effect.
It dilates the pupils of eyes.
It constricts the pupil of eyes.
It decreases salivation.
It increases salivation.
It increases the heartbeat rate.
It decreases the heartbeat rate.
It inhibits gastric and pancreatic activities.
It
stimulates
gastric
and
pancreatic
activities. It accelerates the release of adrenaline and It inhibits the release of adrenaline and noradrenaline.
noradrenaline.
It inhibits peristalsis in the muscles of It stimulates peristalsis in the muscles of stomach, intestine and urinary bladder.
stomach and urinary bladder.
It results in constriction of blood vessels of It results in dilation of blood vessels. skin and visceral organs. It stimulates sweat glands. 10.
It stimulates tear glands.
Reflex arc and reflex action:There are certain body responses which are immediate and do not require any processing by the brain. These responses or actions are controlled by the spinal cord. These are called reflex actions.
Components of a reflex arc
STEPS____________________________________________________________ 3 Get free chapterwise tests for Class Xth on www.tcyonline.com
STEPS … A T C Y P r og r am _______________________________________________________________________________________ LECTURE NOTES – BIOLOGY
Stimulus received by the sensory receptors
Impulse is generated and carried along by sensory neurons toward the spinal cord
Impulse travels through spinal nerves toward the spinal cord along the dorsal root
Impulse arrives at the nerve endings of sensory neurons In the grey matter of the spinal cord
Nerve endings release neurotransmitter. The impulse pass across the relay neuron to the motor neuron
Impulse travels along motor neurons away from the Spinal cord along the ventral root
The nerve endings of motor neuron connect effector organ or muscle
Response produced by effector organ or muscle
Sequence of events in a reflex arc
4 STEPS____________________________________________________________ Get free chapterwise tests for Class Xth on www.tcyonline.com
STEPS … A T CY Pr ogr am _______________________________________________________________________________________ LECTURE NOTES – BIOLOGY
A reflex action may be defined as a spontaneous, automatic and mechanical response to a stimulus controlled by the spinal cord without the involvement of brain. The pathway followed by sensory and motor nerves in a reflex action is called reflex arc. The entire sequence of events that constitute a reflex arc are summarized in above figure. Components of a reflex arc A reflex arc has four main components. 1.
Receptor or sensory organ to perceive the stimulus.
2.
Sensory or afferent nerve which carrie the message from receptor to the spinal cord.
3.
Relay or internuncial neurons of the spinal cord which transmit impulses from the afferent neurons to the efferent neurons.
4.
Motor or efferent nerve which carries the message from the spinal cord to the muscles or glands (effector organ)
Some common examples of reflex action 1.
Blinking of eyes in response to a foreign particle that has entered the eye.
2.
Sneezing or coughing, if any unwanted particle enters the nose or throat.
3.
Watering of mouth at the sight of tasty food.
4.
Immediate withdrawal of hand if a person touches a hot object unknowingly.
5.
Withdrawal of the leg by a man walking barefeet if he steps on a nail.
11.
Pituitary gland & its hormones:
Endocrine glands
Principal functions
Hormone secreted
and their location Pituitary Gland It has three lobes. It is attached to the lower surface of the brain.
Growth Hormone (GH) Controls the overall growth of the
Anterior Lobe
or
Somatotrophic body, muscles and bone. Lack of this
Hormone (STH)
hormone
(hypoactivity)
excessive making
growth the
of
person
causes
long very
bones tall
(gigantism)
STEPS____________________________________________________________ 5 Get free chapterwise tests for Class Xth on www.tcyonline.com
STEPS … A T C Y P r og r am _______________________________________________________________________________________ LECTURE NOTES – BIOLOGY
Adrenocorticotrophic
Controls the growth and function of
Hormone (ACTH)
adrenal cortex. Stimulates secrete
the
adrenal
steroid
cortex
hormones
to
called
glucocorticoids. Thyroid
Stimulating Controls the growth and functioning
Hormone (TSH)
of the thyroid gland. Stimulates the thyroid gland to produce thyroxine.
Follicle
Stimulating In males, it stimulates the process of
Hormone (FSH)
spermatogenesis. In females, it stimulates the follicle cells in the ovaries to develop into mature eggs and also stimulates them to produce oestrogen.
Luteinizing Hormone In males, it stimulates the secretion (LH)
of
male
which
hormone,
in
appearance
turn of
characteristics.
testosterone, influences
secondary In
the
sexual
females,
it
stimulates the secretion of oestrogen and progesterone, which in turn influence the process and ovulation, formation and maintenance of corpus luteum and appearance of secondary sexual characteristics. Prolactin (PRL)
Hormone It
enhances
mammary
gland
development and milk production in females.
Middle Lobe
Melanocyte
Controls the production of melanin
Stimulating Hormone pigment Posterior Lobe
in
the
skin
which
is
(MSH)
responsible for skin colour.
Oxytocin
Controls the vigorous contraction of uterine muscles at the time of child birth. It also helps in milk ejection from the mammary
glands
to
provide
nourishment for the new born during feeding. Vasopressin
or Controls reabsorption of water in
Antidiuretic Hormone kidney tubules. (ADH) 6 STEPS____________________________________________________________ Get free chapterwise tests for Class Xth on www.tcyonline.com
STEPS … A T CY Pr ogr am _______________________________________________________________________________________ LECTURE NOTES – BIOLOGY
12.
Feedback mechanism of hormone secretion:As we know, hormones are required for various functions in our body. To perform these functions a particular hormone may be required in a particular amount at a particular time, for which a control system is required.
Feedback system to control the metabolic rate Any control system should have a feedback mechanism to prevent excessive reaction or over – reaction. For example, the hypothalamus produces the releasing hormone for thyroid stimulating hormone (TSH – RH), which in turn stimulates the pituitary to produce thyroid stimulating hormone (TSH). The TSH activates the thyroid gland to secrete thyroxine. If the level of thyroxine in the blood is less than normal, it has a positive feedback effect on the hypothalamus and pituitary to produce more TSH – RH and TSH, respectively. If the level of thyroxine is more than normal in the blood, a negative feedback effect is seen on the hypothalamus and the pituitary so that they produce less of TSH – RH and TSH, respectively. Positive vertebrates as they lead to instability. Thyroid stimulating hormone (TSH) and thyroxine regulate each other’s level just like the requirement – supply kind of situation. Such a system of opposing effects leads to proper control and balance in a system. The two opposing systems work in coordination and help the body to adjust its output accordingly. The ultimate effect of such a feedback system is homeostasis.
STEPS____________________________________________________________ 7 Get free chapterwise tests for Class Xth on www.tcyonline.com
STEPS … A T C Y P r og r am _______________________________________________________________________________________ LECTURE NOTES – BIOLOGY
13.
Outline of Human nervous system
Peripheral nervous system
Central nervous system
Brain
Spinal cord
Sensory (afferent) nerves
Somatic nervous system
Motor (efferent) nerves
autonomic nervous system
Sympathetic
14.
Parasympathetic
Neuron The functional unit of the nervous system is a highly specialized cell called the nerve cell or neuron. Each nerve cell consists of three principal parts. 1.
Cell body cyton
2.
Axon
3.
Dendrites
The cell body or cyton has a large, central nucleus surrounded by the cytoplasm. In the cytoplasm, nissl granules and neurofibrils are present. Cell organelles like mitochondria, golgi apparatus, andoplasmic reticulum, microfilaments and microtubules, are also present in the cytoplasm.
Structure of a neuron (nerve cell)
Several short, thread – like branches called dendrites (Greek: dendron means tree) arise from the cell body. One of the branches grows very large in comparison to others. This branch is called the axon. The axon is covered o the outside by three layers. 8 STEPS____________________________________________________________ Get free chapterwise tests for Class Xth on www.tcyonline.com
STEPS … A T CY Pr ogr am _______________________________________________________________________________________ LECTURE NOTES – BIOLOGY
1.
Axolemma (the innermost layer)
2.
Myelin sheath or medullary sheath (the middle layer)
3.
Neurilemma (the outermost layer)
The axolemma and neurilemma are continuous sheaths, whereas the myelin sheath is not a continuous one. It is constricted at intervals. These constrictions are known as nodes of Ranvier. The axon ends in axon endings. 15.
Human brain (parts) The human brain is divisible into three major divisions: 1.
Forebrain
2.
Midbrain
3.
Hindbrain
Parts of the human brain
16.
Regions of Cerebrums
Different regions of the cerebrum are associated with different functions
STEPS____________________________________________________________ 9 Get free chapterwise tests for Class Xth on www.tcyonline.com
STEPS … A T C Y P r og r am _______________________________________________________________________________________ LECTURE NOTES – BIOLOGY
17.
EEG:- Our brain is continuously sending out certain waves. These waves differ in their nature at different times, such as while we sleep, when we close our eyes, when we read and so on. This activity of the brain can be recorded with the help of an instrument called electroencephalograph. While recording brain waves, electrodes are taped to different parts of the scalp and the activity of the brain is recorded in the form of an electerocephalogram (EEG).
18.
Types of nerves:There are three types of nerve fibres depending upon the direction in which they transmit the nerve impulse. Sensory nerves. These are also called afferent nerves (Latin: afferent means carry toward). These nerves contain neurons which carry message (impulse) from sensory areas toward the central nervous system. Motor nerves. These are also called efferent nerves (Latin: efferent means carry away). These nerves contain neurons which take messages away from the central nervous system towards the effector organ, such as muscles and glands. Mixed nerves. There are many nerves which are comprised of both afferent (sensory) and efferent (motor) nerve fibres. These are called mixed nerves. For example, most cranial and spinal nerves are called mixed nerves.
19.
Auxins:- Auxins (Greek: auxein means to increase) are a group of plant growth regulators discovered by a Dutch botanist, F.W. Went, in 1928.
Auxins are
synthesized in the shoot apex and young leaves of the plant. These chemicals move from cell to cell by the process of diffusion. IAA (Indole acetic tic acid) is a type of auxin which is concerned with cell enlargement. High auxin concentration stimulates growth on the lower side so the shoot grows upward
Auxins control the geotropic behaviour of a plant.
Functions of auxins 1.
Geotropism. The root of a plant is positively geotropic, i.e. grows downward and the shoot is negatively geotropic, i.e. grows upward. Auxins help to control the geotropic behaviour of the shoot and the root of a plant.
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STEPS … A T CY Pr ogr am _______________________________________________________________________________________ LECTURE NOTES – BIOLOGY
2.
Cell division. Auxins stimulate tissues at the tips of the root and the shoot to undergo rapid cell division.
3.
Cell – elongation. Auxins stimulate considerable cell – enlargement and cell – elongation during the process of growth.
4.
Root formation. The help in root initiation. If auxins are applied artificially, on the cut surface of a stem, root formation is initiated faster.
Auxins can promote root growth in stem cuttings
5.
Parthenocarpy. Auxins play an important role in the development of fruits without pollination and fertilization. This phenomenon is known as parthenocarpy. Fruits produced by this method are called parthenocarpic or seedless fruits.
6.
Apical dominance. Terminal buds have an inhibitory effect on the growth of lateral buds. This is due to the auxins produced at the tip of stem which travel down and inhibit the growth of lateral buds. This phenomenon is called apical dominance. Auxins promote apical dominance in plants.
7.
Leaf and fruit fall. Auxins play an important role in the prevention of preharvest fruit fall in plants like apple, pear, etc. This saves lakhs of rupees due to delayed formation of the abscission layer that is responsible for fall of fruits and leaves.
8.
Enhance
physiological
activities.
Auxins enhance many physiological
processes like protein synthesis, protoplasmic permeability, water uptake, cytoplasmic streaming, respiration, seed germination, etc. 9.
Promote
reproductive
processes.
Auxins
promote
various
processes
associated like flowering, pollen grain germination, fertilization and fruit development. 20.
Photoperiodism:In temperate areas, length of the day varies from 9 – 15 hours during the year. Various phenomena in plants, such as flowering, fruit and seed production, bud and seed dormancy, leaf fall and germination, are under the influence of day length. The most profound change among these is flowering. The importance of photoperiod in flowering was discovered by Garner and Allard in the early 20th century.
STEPS____________________________________________________________ 11 Get free chapterwise tests for Class Xth on www.tcyonline.com
STEPS … A T C Y P r og r am _______________________________________________________________________________________ LECTURE NOTES – BIOLOGY
Plants can be classified, according to their photoperiodic requirement for flowering, into three groups. 1.
Long – day plants
2.
Short – day plants
3.
Day – neutral plants
Classification of plants according to photoperiodic Requirements for flowering
Type
Conditions required for flowering
Short – day plants
Require dark periods longer than a critical length, i.e. days shorter than a critical length,
e.g.
tobacco,
chrysanthemum,
strawberry and soyabean. Long – day plants
Flowering
is
induced
by
dark
periods
shorter than a critical length, e.g. henbane, cabbage, snapdragon and springwheat Day – neutral plants
Flowering
is
independent
of
the
photoperiod, e.g. cucumber, tomato, garden pea, maize and cotton. 21.
Pheromones:- Insects like ants, honey bees, and some other animals like rabbits, communicate through chemicals called pheromones. Have you seen ants walking one behind the other in a trail? They secret pheromones from their anal region. Due to the smell of this chemical they move in straight line.
12 STEPS____________________________________________________________ Get free chapterwise tests for Class Xth on www.tcyonline.com
CONTROL & COORDINATION 1.
Parthenocarpy:- Auxins play an important role in the development of fruits without
pollination
and
fertilization.
This
phenomenon
is
known
as
parthenocarpy. Fruits produced by this method are called parthenocarpic or seedless fruits. 2.
Synapse:- The loose connection between the axon endings of one nerve cell and cyton of the next nerve cell is called synapse. In other words, signals travel from one neuron to another neuron across a junction called synapse. Structure of the synapse The neurons do not touch at the synapse. There is a space between adjacent neurons called the synaptic cleft. The synaptic cleft is about 20 mm in width. The axon terminal of a presynaptic neuron has a bulb – like appearance known as synaptic bulb.
Structure of the synapse
3.
Homeostasis:- The capacity of an organism to adjust itself to cope with the external stress and maintain a steady state of functioning is referred to as homoeostasis. (Latin: homeo means similar, statis means situation) Homeostasis in a multicellular organism is achieved in two ways. 1.
By the endocrine system
2.
By the nervous system
Both hormones and nerve impulses coordinate the body’s activities, but they do so in different ways.
STEPS____________________________________________________________ 1 Get free chapterwise tests for Class Xth on www.tcyonline.com
STEPS … A T C Y P r og r am _______________________________________________________________________________________ LECTURE NOTES – BIOLOGY
4.
Endocrine glands: endo means within, krinein means to separate. As these glands do not have their own ducts, the secretions of such glands, hormones, are released directly into the tissue space next to each endocrine cell and are carried by blood or lymph to the target organ.
Blood flow
Glands with and without ducts 5.
Efferent nerve:- Motor or efferent nerve which carries the message from the spinal cord to the muscles or glands (effector organ)
6.
Afferent nerve:- Sensory or afferent nerve which carries the message from receptor to the spinal cord.
7.
Neurotransmitters:- The transmission across a synapse is by chemical means. The synaptic bulb contains chemicals known neurotransmitters. When a nerve impulse (action potential) arises at the axon terminal, it causes synaptic bulbs
to
release
neurotransmitters
in
the
synaptic
cleft.
These
neurotransmitters diffuse easily across the synaptic cleft. In this way, the impulse is transmitted to another nerve cell or neuron. There are many neurotransmitters
but
the
principle
ones
are
acetylcholine
and
norepinephrine. 8.
Names of Pythohormones:- There are five main types of naturally occurring plant growth regulators. 1.
Auxins
2.
Gibberellins
3.
Kinins
4.
Ethylene
5.
Abscisic acid (ABA)
2 STEPS____________________________________________________________ Get free chapterwise tests for Class Xth on www.tcyonline.com
STEPS … A T CY Pr ogr am _______________________________________________________________________________________ LECTURE NOTES – BIOLOGY
9.
Differences between sympathetic and parasympathetic nervous systems Parasympathetic nervous system
Sympathetic nervous system
The nerve fibres originate in the middle The nerve fibres originate from the brain portion – thoracic and lumbar region, of the and lower (sacral) region of the spinal cord. spinal cord. The ganglia are in a chain running parallel The ganglia are near or in the target organ. and close to spinal cord. Inhibitory (calming down) effect.
Stimulatory effect.
It dilates the pupils of eyes.
It constricts the pupil of eyes.
It decreases salivation.
It increases salivation.
It increases the heartbeat rate.
It decreases the heartbeat rate.
It inhibits gastric and pancreatic activities.
It
stimulates
gastric
and
pancreatic
activities. It accelerates the release of adrenaline and It inhibits the release of adrenaline and noradrenaline.
noradrenaline.
It inhibits peristalsis in the muscles of It stimulates peristalsis in the muscles of stomach, intestine and urinary bladder.
stomach and urinary bladder.
It results in constriction of blood vessels of It results in dilation of blood vessels. skin and visceral organs. It stimulates sweat glands. 10.
It stimulates tear glands.
Reflex arc and reflex action:There are certain body responses which are immediate and do not require any processing by the brain. These responses or actions are controlled by the spinal cord. These are called reflex actions.
Components of a reflex arc
STEPS____________________________________________________________ 3 Get free chapterwise tests for Class Xth on www.tcyonline.com
STEPS … A T C Y P r og r am _______________________________________________________________________________________ LECTURE NOTES – BIOLOGY
Stimulus received by the sensory receptors
Impulse is generated and carried along by sensory neurons toward the spinal cord
Impulse travels through spinal nerves toward the spinal cord along the dorsal root
Impulse arrives at the nerve endings of sensory neurons In the grey matter of the spinal cord
Nerve endings release neurotransmitter. The impulse pass across the relay neuron to the motor neuron
Impulse travels along motor neurons away from the Spinal cord along the ventral root
The nerve endings of motor neuron connect effector organ or muscle
Response produced by effector organ or muscle
Sequence of events in a reflex arc
4 STEPS____________________________________________________________ Get free chapterwise tests for Class Xth on www.tcyonline.com
STEPS … A T CY Pr ogr am _______________________________________________________________________________________ LECTURE NOTES – BIOLOGY
A reflex action may be defined as a spontaneous, automatic and mechanical response to a stimulus controlled by the spinal cord without the involvement of brain. The pathway followed by sensory and motor nerves in a reflex action is called reflex arc. The entire sequence of events that constitute a reflex arc are summarized in above figure. Components of a reflex arc A reflex arc has four main components. 1.
Receptor or sensory organ to perceive the stimulus.
2.
Sensory or afferent nerve which carrie the message from receptor to the spinal cord.
3.
Relay or internuncial neurons of the spinal cord which transmit impulses from the afferent neurons to the efferent neurons.
4.
Motor or efferent nerve which carries the message from the spinal cord to the muscles or glands (effector organ)
Some common examples of reflex action 1.
Blinking of eyes in response to a foreign particle that has entered the eye.
2.
Sneezing or coughing, if any unwanted particle enters the nose or throat.
3.
Watering of mouth at the sight of tasty food.
4.
Immediate withdrawal of hand if a person touches a hot object unknowingly.
5.
Withdrawal of the leg by a man walking barefeet if he steps on a nail.
11.
Pituitary gland & its hormones:
Endocrine glands
Principal functions
Hormone secreted
and their location Pituitary Gland It has three lobes. It is attached to the lower surface of the brain.
Growth Hormone (GH) Controls the overall growth of the
Anterior Lobe
or
Somatotrophic body, muscles and bone. Lack of this
Hormone (STH)
hormone
(hypoactivity)
excessive making
growth the
of
person
causes
long very
bones tall
(gigantism)
STEPS____________________________________________________________ 5 Get free chapterwise tests for Class Xth on www.tcyonline.com
STEPS … A T C Y P r og r am _______________________________________________________________________________________ LECTURE NOTES – BIOLOGY
Adrenocorticotrophic
Controls the growth and function of
Hormone (ACTH)
adrenal cortex. Stimulates secrete
the
adrenal
steroid
cortex
hormones
to
called
glucocorticoids. Thyroid
Stimulating Controls the growth and functioning
Hormone (TSH)
of the thyroid gland. Stimulates the thyroid gland to produce thyroxine.
Follicle
Stimulating In males, it stimulates the process of
Hormone (FSH)
spermatogenesis. In females, it stimulates the follicle cells in the ovaries to develop into mature eggs and also stimulates them to produce oestrogen.
Luteinizing Hormone In males, it stimulates the secretion (LH)
of
male
which
hormone,
in
appearance
turn of
characteristics.
testosterone, influences
secondary In
the
sexual
females,
it
stimulates the secretion of oestrogen and progesterone, which in turn influence the process and ovulation, formation and maintenance of corpus luteum and appearance of secondary sexual characteristics. Prolactin (PRL)
Hormone It
enhances
mammary
gland
development and milk production in females.
Middle Lobe
Melanocyte
Controls the production of melanin
Stimulating Hormone pigment Posterior Lobe
in
the
skin
which
is
(MSH)
responsible for skin colour.
Oxytocin
Controls the vigorous contraction of uterine muscles at the time of child birth. It also helps in milk ejection from the mammary
glands
to
provide
nourishment for the new born during feeding. Vasopressin
or Controls reabsorption of water in
Antidiuretic Hormone kidney tubules. (ADH) 6 STEPS____________________________________________________________ Get free chapterwise tests for Class Xth on www.tcyonline.com
STEPS … A T CY Pr ogr am _______________________________________________________________________________________ LECTURE NOTES – BIOLOGY
12.
Feedback mechanism of hormone secretion:As we know, hormones are required for various functions in our body. To perform these functions a particular hormone may be required in a particular amount at a particular time, for which a control system is required.
Feedback system to control the metabolic rate Any control system should have a feedback mechanism to prevent excessive reaction or over – reaction. For example, the hypothalamus produces the releasing hormone for thyroid stimulating hormone (TSH – RH), which in turn stimulates the pituitary to produce thyroid stimulating hormone (TSH). The TSH activates the thyroid gland to secrete thyroxine. If the level of thyroxine in the blood is less than normal, it has a positive feedback effect on the hypothalamus and pituitary to produce more TSH – RH and TSH, respectively. If the level of thyroxine is more than normal in the blood, a negative feedback effect is seen on the hypothalamus and the pituitary so that they produce less of TSH – RH and TSH, respectively. Positive vertebrates as they lead to instability. Thyroid stimulating hormone (TSH) and thyroxine regulate each other’s level just like the requirement – supply kind of situation. Such a system of opposing effects leads to proper control and balance in a system. The two opposing systems work in coordination and help the body to adjust its output accordingly. The ultimate effect of such a feedback system is homeostasis.
STEPS____________________________________________________________ 7 Get free chapterwise tests for Class Xth on www.tcyonline.com
STEPS … A T C Y P r og r am _______________________________________________________________________________________ LECTURE NOTES – BIOLOGY
13.
Outline of Human nervous system
Peripheral nervous system
Central nervous system
Brain
Spinal cord
Sensory (afferent) nerves
Somatic nervous system
Motor (efferent) nerves
autonomic nervous system
Sympathetic
14.
Parasympathetic
Neuron The functional unit of the nervous system is a highly specialized cell called the nerve cell or neuron. Each nerve cell consists of three principal parts. 1.
Cell body cyton
2.
Axon
3.
Dendrites
The cell body or cyton has a large, central nucleus surrounded by the cytoplasm. In the cytoplasm, nissl granules and neurofibrils are present. Cell organelles like mitochondria, golgi apparatus, andoplasmic reticulum, microfilaments and microtubules, are also present in the cytoplasm.
Structure of a neuron (nerve cell)
Several short, thread – like branches called dendrites (Greek: dendron means tree) arise from the cell body. One of the branches grows very large in comparison to others. This branch is called the axon. The axon is covered o the outside by three layers. 8 STEPS____________________________________________________________ Get free chapterwise tests for Class Xth on www.tcyonline.com
STEPS … A T CY Pr ogr am _______________________________________________________________________________________ LECTURE NOTES – BIOLOGY
1.
Axolemma (the innermost layer)
2.
Myelin sheath or medullary sheath (the middle layer)
3.
Neurilemma (the outermost layer)
The axolemma and neurilemma are continuous sheaths, whereas the myelin sheath is not a continuous one. It is constricted at intervals. These constrictions are known as nodes of Ranvier. The axon ends in axon endings. 15.
Human brain (parts) The human brain is divisible into three major divisions: 1.
Forebrain
2.
Midbrain
3.
Hindbrain
Parts of the human brain
16.
Regions of Cerebrums
Different regions of the cerebrum are associated with different functions
STEPS____________________________________________________________ 9 Get free chapterwise tests for Class Xth on www.tcyonline.com
STEPS … A T C Y P r og r am _______________________________________________________________________________________ LECTURE NOTES – BIOLOGY
17.
EEG:- Our brain is continuously sending out certain waves. These waves differ in their nature at different times, such as while we sleep, when we close our eyes, when we read and so on. This activity of the brain can be recorded with the help of an instrument called electroencephalograph. While recording brain waves, electrodes are taped to different parts of the scalp and the activity of the brain is recorded in the form of an electerocephalogram (EEG).
18.
Types of nerves:There are three types of nerve fibres depending upon the direction in which they transmit the nerve impulse. Sensory nerves. These are also called afferent nerves (Latin: afferent means carry toward). These nerves contain neurons which carry message (impulse) from sensory areas toward the central nervous system. Motor nerves. These are also called efferent nerves (Latin: efferent means carry away). These nerves contain neurons which take messages away from the central nervous system towards the effector organ, such as muscles and glands. Mixed nerves. There are many nerves which are comprised of both afferent (sensory) and efferent (motor) nerve fibres. These are called mixed nerves. For example, most cranial and spinal nerves are called mixed nerves.
19.
Auxins:- Auxins (Greek: auxein means to increase) are a group of plant growth regulators discovered by a Dutch botanist, F.W. Went, in 1928.
Auxins are
synthesized in the shoot apex and young leaves of the plant. These chemicals move from cell to cell by the process of diffusion. IAA (Indole acetic tic acid) is a type of auxin which is concerned with cell enlargement. High auxin concentration stimulates growth on the lower side so the shoot grows upward
Auxins control the geotropic behaviour of a plant.
Functions of auxins 1.
Geotropism. The root of a plant is positively geotropic, i.e. grows downward and the shoot is negatively geotropic, i.e. grows upward. Auxins help to control the geotropic behaviour of the shoot and the root of a plant.
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2.
Cell division. Auxins stimulate tissues at the tips of the root and the shoot to undergo rapid cell division.
3.
Cell – elongation. Auxins stimulate considerable cell – enlargement and cell – elongation during the process of growth.
4.
Root formation. The help in root initiation. If auxins are applied artificially, on the cut surface of a stem, root formation is initiated faster.
Auxins can promote root growth in stem cuttings
5.
Parthenocarpy. Auxins play an important role in the development of fruits without pollination and fertilization. This phenomenon is known as parthenocarpy. Fruits produced by this method are called parthenocarpic or seedless fruits.
6.
Apical dominance. Terminal buds have an inhibitory effect on the growth of lateral buds. This is due to the auxins produced at the tip of stem which travel down and inhibit the growth of lateral buds. This phenomenon is called apical dominance. Auxins promote apical dominance in plants.
7.
Leaf and fruit fall. Auxins play an important role in the prevention of preharvest fruit fall in plants like apple, pear, etc. This saves lakhs of rupees due to delayed formation of the abscission layer that is responsible for fall of fruits and leaves.
8.
Enhance
physiological
activities.
Auxins enhance many physiological
processes like protein synthesis, protoplasmic permeability, water uptake, cytoplasmic streaming, respiration, seed germination, etc. 9.
Promote
reproductive
processes.
Auxins
promote
various
processes
associated like flowering, pollen grain germination, fertilization and fruit development. 20.
Photoperiodism:In temperate areas, length of the day varies from 9 – 15 hours during the year. Various phenomena in plants, such as flowering, fruit and seed production, bud and seed dormancy, leaf fall and germination, are under the influence of day length. The most profound change among these is flowering. The importance of photoperiod in flowering was discovered by Garner and Allard in the early 20th century.
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Plants can be classified, according to their photoperiodic requirement for flowering, into three groups. 1.
Long – day plants
2.
Short – day plants
3.
Day – neutral plants
Classification of plants according to photoperiodic Requirements for flowering
Type
Conditions required for flowering
Short – day plants
Require dark periods longer than a critical length, i.e. days shorter than a critical length,
e.g.
tobacco,
chrysanthemum,
strawberry and soyabean. Long – day plants
Flowering
is
induced
by
dark
periods
shorter than a critical length, e.g. henbane, cabbage, snapdragon and springwheat Day – neutral plants
Flowering
is
independent
of
the
photoperiod, e.g. cucumber, tomato, garden pea, maize and cotton. 21.
Pheromones:- Insects like ants, honey bees, and some other animals like rabbits, communicate through chemicals called pheromones. Have you seen ants walking one behind the other in a trail? They secret pheromones from their anal region. Due to the smell of this chemical they move in straight line.
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